An ab initio quantum chemical investigation of solvent-induced effect on 14 N-NQR parameters of alanine, glycine, valine, and serine using a polarizable continuum model

In this paper ab initio quantum mechanical calculations of the 14N-nuclear quadrupole resonance (NQR) parameters of alanine, glycine, valine, and serine obtained from an electric field gradient (EFG) tensor, such as quadrupole frequencies and asymmetry parameters in gas phase and different solvents, have been carried out with the Gaussian 98 software package and the solvent-induced effects on these parameters have been evaluated using density functional theory (DFT). Furthermore, direct and indirect solvent effects on asymmetry parameters have been also calculated. We determined that the NQR parameters of the nitrogen atoms of amino acids are highly sensitive to environmental effects and that the observed solvent-induced shielding variation is strongly related to the values of the dielectric constants of the solvent and whether it is protic or aprotic. For more investigation of the solvent effect, the relative energies of each amino acid in various solvents have been calculated and the graphs of the relative energies versus dielectric constants have been analyzed.